VLF atmospherics in relation to winter thunderstorms

Simultaneous studies on 10 and 20 kHz over the tropical region Calcutta show that VLF atmospherics are intimately related with winter thunderstorms. In the record, the sudden enhancement of the integrated field intensity of atmospherics preceded by an initial gradual rise seems to be closely associated with the developmental stage of thunderclouds while the steady recover marking its decay starts with a sudden decrease indicating the vanishing of its bipolar structure associated with rainfall. The maximum activity of winter thunderstorms as indicated by the atmospherics occur at local afternoon.